uses
 ShellAPI;

function InstallINF(const PathName: string; hParent: HWND): Boolean;
var
 instance: HINST;
begin
 instance := ShellExecute(hParent,
 PChar('open'),
 PChar('rundll32.exe'),
 PChar('setupapi,InstallHinfSection DefaultInstall 132 ' + PathName),
 nil,
 SW_HIDE);

 Result := instance > 32;
end; { InstallINF }

// Example:

procedure TForm1.Button1Click(Sender: TObject);
begin
 InstallINF('C:\DelphiWorld.inf', 0);
end;